Seattle's 2 Line light rail crossing of Lake Washington represents a first in transportation engineering: the world's only passenger rail system operating on a floating bridge. Built on the Interstate 90 Homer M. Hadley Memorial floating bridge, the crossing enables trains to travel at their planned speed of 55 mph across a structure that is constantly moving due to wind, waves and changing water levels.

To make the crossing possible, WSP led a team of engineers that developed innovative solutions to strengthen the bridge, maintain precise rail alignment and protect critical infrastructure from corrosion. A unique, specialized track system uses continuous welded rail and a combination of customized bearings that accommodate bridge movement while delivering a smooth ride for passengers. As Matthew Barber of WSP noted, the so-called Curved Element Support Rail, or CESuRa, track bridge system distributes force and motion through the track structure, resulting in nearly imperceptible rail and vehicle movement.

Combined with advanced monitoring technologies and a digital twin of the bridge, the project demonstrates how engineering innovation can overcome complex infrastructure challenges while expanding transportation connectivity across the region.